Broadband telecommunications solutions such as digital subscriber line (DSL) and/or other broadband cable connections (e.g. cable modem solutions) are widely used for providing IP-connectivity to a large public. Asynchronous digital subscriber line (ADSL) as an example, is a data communications technology that enables fast data transmission over regular copper lines such as subscriber lines for use with analog plain old telecommunications services (POTS). Also widely used are cable modem services, which are designed to modulate a data signal over cable television infrastructure providing broadband Internet access to users at home. In addition, wireless broadband telecommunications services are emerging fast, such as local multipoint distribution service (LMDS), multichannel multipoint distribution service (MMDS), worldwide interoperability for microwave access (WiMAX) and high performance radio metropolitan area network (HIPERMAN).
Most broadband services are sufficiently fast for providing not only fast internet connections but also real time contiguous data services. Examples of such services are voice over IP, online interactive gaming and other interactive services such as remote control of processes via a data network. Other services that may be considered involve streaming video and audio. Providing these services mostly requires a contiguous flow of data streaming between a sender and a receiver, in order to establish a signal comprising sufficient data and providing it at a rate sufficiently to keep up the quality. Since these services are often highly delay-sensitive, in this respect meaning that the data must be received shortly after sending thereof, they may be identified as real time services. Hereinafter, such services shall be referred to real time contiguous data services.
Most data communications services can be divided in four classes, e.g. as defined for universal mobile telecommunications system (UMTS) by 3GPP in 3GPP TS 23.107 v3.9.0 (September 2002)—“3rd Generation Partnership Project; Technical Specification Group Services and System Aspects; Quality of Service (QoS) concept and architecture (Release 1999)”: conversational class, streaming class, interactive class and background class. These classes define the sensibility of data services to quality of service.
Conversational and streaming classes are mainly intended to be used to carry real time traffic flows, including most of the services described above. The main divider between conversational and streaming class is their sensitivity to delays in the data traffic. Both classes of services are sensitive to delay in the data traffic, however the required level of quality of service is determined by human perception in case of conversational class services.
Conversational class services include for example voice over IP and video conferencing. It is mainly characterized by the fact that real time conversation is performed between peers (or groups) of life (human) end users. Real time conversation scheme is characterized by that the transfer time shall be low because of the conversational nature of the scheme and at the same time that the time relation (variation) between information entities of the stream shall be preserved in the same way as for real time streams. The maximum transfer delay is given by the human perception of video and audio conversation. Therefore the limit for acceptable transfer delay is very strict, as failure to provide low enough transfer delay will result in unacceptable lack of quality.
Streaming class services include real time video and/or audio for example. When the user is looking at, or listening to, real time video or audio, the scheme of real time streams applies. The real time data flow is always aiming at a life (human) destination. It is a single one-way transport and is therefore not interactive. The streaming class service scheme is one of the newcomers in data communication, raising a number of new requirements in both telecommunication and data communication systems. It is characterized by that the time relations (variations) between information entities (i.e. samples, packets) within a flow shall be preserved, although is does not have any requirements on low overall transfer delay. The delay variation of end to end flow must be limited to preserve the time relation (variation) between information entities in the stream. But as the stream normally is time aligned at the receiving end (in the user equipment), the highest acceptable delay variation over the transmission media is given by the capability of the time alignment function of the application. Compared to conversational class. Acceptable delay variations are thus much greater than the delay variation given by the limits of human perception.
Interactive class service scheme applies when the end user, which may be either a machine or a human, is online requesting data from remote equipment (e.g. a server) for instance. Examples of human interaction with remote equipment are: web browsing, data base retrieval, server access, etc. Examples of machines interactions with remote equipment are polling for measurement records and automatic data base enquiries (telematics). Interactive class traffic is a data communication scheme that on an overall level is characterized by the request response pattern of the end user. At the message destination there is an entity expecting the message (response) within a certain time. Round trip delay time is therefore one of the key attributes. Another characteristic is that the content of the packets shall be transparently transferred (with low bit error rate).
The background class service scheme applies when the end user (typically a computer) sends and receives data files in the background. Examples are background delivery of e-mails, short message service (SMS), download of data bases and reception of measurement records. Background class traffic is a data communication scheme that on an overall level is characterized by that the destination is not expecting the data within a certain time. The scheme is thus more or less delivery time insensitive. Another characteristic is that the content of the packet shall be transparently transferred (with low bit error rate). As is clear from the above definition and description of the service classes (conversational class, streaming class, interactive class and background class), the conversational class and streaming class services are characterized by contiguously filling data from end to end. For conversational class services, the requirements are so strict that on a packet switched network, the data packages must be offered in their original order to the user of the conversational class service, without a noticeable interruption by the user. For streaming class services the requirements are less strict, but still the packages must be presented to the user in a streaming fashion without a noticeable interruption, and preferably shortly after the sending thereof.
On the other hand, interactive class and background class services may have requirements with respect to the time of arrival of data packages, however there is no requirement for data flowing contiguously and having to be presented in the streaming fashion having an unnoticeable interruption.
Summarizing the above for real time contiguous data services, these services may be divided in interactive (conversational class) service and non-interactive (streaming class) services. The interactive services require fast two-way communications with low overall delay and only limited variation in time of arrival of information entities. The non-interactive services mainly require limited variation in time of arrival of information entities, while a certain overall delay may still be acceptable. Voice over IP and video conferencing, or streaming audio/video may easily be divided in these two real time contiguous data service classes. It is noted that interactive multi-user gaming is typically is a conversational class service of which the transmission requirements are determined by human perception.
In view of the above and with respect to real time contiguous data services, it will be understood that the quality of service requirement for data connections for providing conversational class data services are more strict than for streaming class data services, and similarly, the quality of service requirement for data connections for providing streaming class data services are more strict than for interactive data services (including multi-user gaming). The background class services are the least sensitive to inferior quality of service.
At present, some conversational and streaming class real time contiguous data services are available but are not widely used by the public due to the fact that, although the quality of service of the broadband connections may be sufficient, internet performance is not sufficiently reliable to provide quality real time contiguous data services. It is however to be expected that as a result of continuous improvement of performance, the exploitation of real time contiguous data services to a large public is simply a matter of time.
Most data communications networks, including the internet, are packet switched data networks. Data which is to be sent via a packet switched data network is divided in data packages which are then sent out onto the network. In each network node, packages are forwarded to a next network node which is closer to the destination of the packet. Eventually, a packet arrives at its destination where it will be reassembled with other received data packages to provide the data collection that was originally sent, e.g. a data file. Networks of this type are also called datagram networks.
At transport level in the open system interconnection model (OSI-model), services are mostly provided using either transmission control protocol (TCP) or user datagram protocol (UDP). Real time contiguous data services belonging to conversational and streaming class are most often provided using the (more efficient) UDP protocol. UDP does not have a retransmission or resequencing mechanism. A packet received late is simply considered lost.
In particular, for real time contiguous data services, UDP is mostly used as the protocol within the transport layer, in combination with real time transport protocol (RTP) in the session layer and above the session layer in the presentation layer, real time streaming protocol (RTSP) is used to present the data stream to the application in the application layer. It is however noted that it may be possible to use TCP protocol for providing real time contiguous data services, instead of UDP. For example, this may be the case for multi-user online gaming.
Since UDP does not have re-sequencing or re-transmission mechanism, this may be provided in higher layers of the OSI-model. Amongst the tasks of RTP and RTSP, a re-sequencing mechanism may be provided for depending on the application. It will be understood that such a re-sequencing mechanism is optional, and may not provide any added value to the provisioning of some services.
Where the transport layer is responsible for end to end error recovery and flow control, it is the network layer in the OSI-model below the transport layer responsible for routing of the data packages. Therefore, in the network layer, the contents of a data package is transparent and each package comprises a header providing details regarding its destination (comparable to a regular postage system where packages comprise an address label but their contents is transparent to the courier).
In the data link layer of the OSI-model, below the network layer, data packages are encoded en decoded into bits. It is the data link layer which is responsible for the actual transmission of the data from a logical perspective. Below the data link layer in the OSI-model, there is the physical layer which is the lowest layer of the OSI-model, responsible for taking care of communication from a hardware perspective (multiplexing, cables, etc.). The data itself is completely irrelevant in the physical layer, since at this level the main requirement is to bring an electrical or optical signal from a first point to a second point and to a next point in the network.
The network managed by the network operator mainly operates within the lower three levels of the OSI-model: physical layer, data link layer and network layer. For more sophisticated tasks, it may be possible to operate on a higher level in the OSI-model, e.g. the transport layer.
For network operators (NO) and internet service providers (ISP), the data received via a broadband connection (such as an ADSL-connection or cable modem connection) which has to be sent via the internet to its destination, is therefore simply received as a stream of data packages without any meaning but having a destination. Each package has a header which enables forwarding the package to a next node closer to it's destination, but since the contents of the data packages is transparent at physical level, data link level, network level or transport level, the underlying data service associated with the data package is not known to the network operator or internet service provider.
This provides the disadvantage for the internet provider and network operator that it is difficult to distinguish the use of real time contiguous data services from the use of any other data service (such as regular web surfing, e-mail or other data services) within the data stream. It therefore becomes impossible to selectively provide conversational and/or streaming class services and other services with a real time contiguous character, such as online multi-user gaming, separately from any other internet services. A user ordering an ADSL-subscriber line or cable modem connection, as a result of the performance of this broadband connection, can use real time contiguous data services just as it can use any other data services provided that the user uses the necessary software and other premises. As a result, it is impossible for the network operator to provide these services separately to a user, and to charge the user for the use of these services.